For some time it has been recognized that it would be desirable to concentrate sunlight into the input end of a light guide, in order to provide solar daylighting deep within the core region of a building. It has been economically unfeasible to implement this concept because, in order to concentrate sunlight to the required extent, it is necessary to counteract the changing direction of the sunlight caused by the sun's apparent motion through the sky. This requires a device known as a "heliostat". Prior art heliostats have been too expensive to justify their use in solar daylighting applications. The present invention provides a novel, inexpensive concentrating heliostat which can be used to implement solar daylighting in an economically feasible manner.